GB836440A - Improvements in or relating to the use of ferrite members in microwave conductors - Google Patents

Abstract

836,440. Non-reciprocal waveguide devices. SPERRY RAND CORPORATION. Nov. 30, 1956 [Dec. 8, 1955 (2)], No. 36698/56. Class 40 (8). A polarized ferrite element is arranged in a waveguide to present zero permeability to circularly - polarized waves travelling in one direction and a finite permeability to circularly-polarized waves travelling in the other direction. The reverse wave is attenuated by virtue of dissipation within the ferrite element. In the embodiment of Fig. 2 the ferrite element 12 is supported centrally within a circular waveguide 11 by annular dielectric members 22 and is polarized by a coil 13 providing an axial magnetic field whose direction is indicated by the arrow. The waveguide 11 is connected to input and output rectangular waveguides 17, 19 and is provided at either end with polarizers 14, 15 of conventional design capable of producing a circularly-polarized wave. The first polarizer 14 is arranged to convert the plane-polarized wave from the input 17 into a counterclockwise rotating wave, i.e. a positively-rotating wave when viewed in the direction of the magnetic field. The outer shell 26, Fig. 4, of the member 12 is made of ferrite and the magnetic field is adjusted to such a value that the ferrite shell presents an effective permeability of zero to a positively-rotating wave. Thus the shell behaves as a cylindrical conductor for the input wave and forms with the waveguide 11 a coaxial line along which the wave is propagated to the polarizer 15. The latter is arranged to reconvert the circularly-polarized wave to a wave plane-polarized in the same plane as the input wave. A wave reflected from the output due to mismatch propagates back through the polarizer 15 and is converted to a circularly polarized wave rotating in a counterclockwise sense, i.e. a negatively rotating wave when viewed in the direction of the field. To such a wave the shell 26 presents a positive permeability and hence the wave propagates within the shell. A layer 28 of dissipative material within the shell produces attenuation of the wave energy. The shell may also contain a core 27 of ferrite. Alternatively, it may be completely filled with a ferrite chosen for its dissipative properties. The tapered end pieces 29, 30 may be of ferromagnetic material coated with a conductive layer. They may be permanent magnets providing the polarizing field for the ferrite element. The invention may be applied to a rectangular waveguide 41, Fig. 6, in which case the ferrite element consists of an elongated block or a series of posts 42, 43, 44 situated at a point in the waveguide offset from the centre-line where the wave is circularly polarized. The rods may be hollow and a lossy dielectric liquid may be circulated through them. In the embodiment of Fig. 9, the non- reciprocal elements are in the form of ferrite members 57, 58 of semi-circular section containing dissipative material. They are placed in contact with conduits 59, 60 for liquid coolant.